<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
    <title>Set 实践</title>
  </head>
  <body>
    <script>
      let arr = [1, 2, 3, 4, 5, 4, 3, 2, 1];
      //1. 数组去重
      //   let result = [...new Set(arr)];
      //   console.log(result);
      //2. 交集
      let arr2 = [4, 5, 6, 5, 6];
      // let result = [...new Set(arr)].filter(item => {
      //     let s2 = new Set(arr2);// 4 5 6
      //     if(s2.has(item)){
      //         return true;
      //     }else{
      //         return false;
      //     }
      // });
      //   let result = [...new Set(arr)].filter((item) => new Set(arr2).has(item));
      //   console.log(result);

      //3. 并集
      let union = [...new Set([...arr, ...arr2])];
      console.log(union);

      //4. 差集
      let diff = [...new Set(arr)].filter((item) => !new Set(arr2).has(item));
      console.log(diff);
    </script>
  </body>
</html>
